Those great big high pressure systems (connoted by an "H") are drifting further south, meaning the cold winter storms (the blue sticks with shark fins) are hitting southern Australia less often. And that may not be very technical but it does kinds explain why July was really warm.Source: Supplied

CLIMATE change is kicking in and it's kicking in fast.

That's the experts' conclusion after a record-breaking July in which all five of Australia's eastern capitals had record high temperatures.

Some of the numbers are truly eye-popping.

Sydney is normally 12.2 degrees at any given moment in July (if you average day and night temperatures). This month it was 14.6. That's 2.4 degrees above the norm.

Melbourne is usually 9.8 in July. This month it was 12.2.

Canberra is normally 5.7. This July it was 7.5. Brisbane is normally 15. This July it was 17.2. Hobart is normally 8.2. This month it was 10.

And on it goes - unprecedented temperature jump after unprecedented temperature jump across a vast geographic area.

Of course, there have always been variations in the past. But nothing like this. Scientists say we are seeing a severe breakdown of normal winter weather patterns in Australia.

"In a normal July you'll have a number of big Southern Ocean storm systems and cold fronts associated with them crossing the southern part of the continent," explains Blair Trewin, climatologist at the Bureau of Meteorology.

"We had just one system like that in July which brought the cold weather the weekend before last. In a normal July you'd be under the influence of that sort of weather for half the month."

Australia has always copped its coldest winter blasts from wild Southern Ocean storms, born in the Antarctic, which lurk in the latitudinal zone which sailors call the 'roaring forties'.

Between June and September, many of those storms have traditionally veered north and sent a chill lasting two or three days through the mid-30s latitudes, where much of southern Australia lies.

But just as 50 is the new 40 in modern life, meteorologists say the roaring 50s are effectively becoming the new roaring 40s. And that means fewer and fewer storms are migrating north to Australia.

"In addition to the overall warming trend, there is a clear trend in both the northern and southern hemispheres where the mid-latitude storm belt is retreating to the poles," Mr Trewin said.

So there's your long-term picture. Not only is it getting warmer overall, the weather systems which bring the coldest weather are retreating.

The short-term picture is that Australia has been surrounded with warmer-than-usual sea surface water this winter. Warmer water tends to translate to warmer temperatures on a day-to-day level.

None of which is to suggest that we won't have cold winters ever again, or ski seasons which are a little more snowy than this year's one is turning out to be. But the numbers reveal a pretty clear trend.

"It would be a dramatic surprise if we saw temperatures two degrees above normal month after month after month," Mr Trewin said.

"This is the sort of anomaly we used to see one month in 50. Now we're seeing it one month in 10."

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Comments on this story

Kate Posted at 5:56 PM July 31, 2013

Hmmm, they obviously haven't spent any time this winter in Perth. One of the coldest in memory ....

Joe Citizen of Melb Posted at 5:55 PM July 31, 2013

Climate change. Isn't that the folly Tony Abbott assures us leads to a tax on an invisible item that doesn't exist....or something utterly ridiculous like that?

Angry_Of_Mayfair Posted at 5:53 PM July 31, 2013

Once again we see the bloody - minded stupidity of the great unwashed masses rearing its ugly head in the likes of Jack Goff. The Dude Of Reality has summed up my thoughts perfectly.

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